Renal System

• The Kidney

  • Convert >1700L of blood per day into ~1L of urine.
  • excretes the waste products of metabolism, precisely regulates the body's concentration of water and salt, maintains the appropriate acid balance of the plasma and serves as an endocrine organ, secreting such hormones as erythropoietin, renin and prostaglandins. 
  • Adult kidney weights ~150g
• Kidney Structure:

  • As the ureter enters the kidney at the hilum, it dilates into a funnel-shaped cavity (pelvis), from which derive 2 or 3 main branches, the major calyces. These subdivide into 3 or 4 minor calyces. 12 minor calyces in a kidney.
  • On the cut surface, the kidney is made up of a cortex and medulla. Cortex is ~1.2-1.5cm in thickness.
  • Medulla consists of renal pyramids, the apices of which are called papillae, each related to a calyx.
  • Cortical tissue extends into spaces between adjacent pyramids as the renal columns of Bertin.

   
• Blood Vessels

  Rich supply.

  Kidneys receive about 25% of the cardiac output.

  Cortex is by far most richly vascularised part of kidney, receiving 90% of total renal blood supply.
• Glomeruli

  • Consists of a network of capillaries lined by endothelium invested by 2 layers of epithelium
  • Visceral epithelium is incorporated into and becomes an intrinsic part of capillary wall, separated from endothelial cells by a basement membrane.
  • Parietal epithelium situated on Bowman's capsule, lines the urinary space, the cavity in which plasma filtrate first collects.
• Glomerular capillary wall is filtering membrane and consist of following structures:

  • A glomerular basement membrane
  • Visceral epithelial cells (podocytes) - possess interdigitating processes embedded in and adherent the basement membrane
  • Entire glomerular tuft is supported by mesangial cells lying between the capillaries
  • A thin layer of fenestrated endothelial cells, each fenestrum being about 70-100nm in diameter
• Tubules function:

  • Proximal tubules = reabsorption of 2/3's of the filtered sodium and water as well as glucose, potassium, phosphate, amino acids and proteins.
  • The juxtaglomerular apparatus lies closely against the glomerulus where the afferent arteriole enters. Consists of:
  • Juxtaglomerular cells, modified granulated smooth muscle cells.
  • Macula densa, a specialised region of the distal tubule
  • Lacis cells, reside in area bounded by the afferent arteriole, the macula densa and the glomerulus.
  • Juxtaglomerular cells are principle source of renin production in kidney.
• Interstitium

  • In normal cortex, the interstitial space is compact, occupied by the fenestrated peritubular capillaries and a small number of fibroblast-like cells.
  • Any obvious expansion of the cortical interstitium is usually abnormal
  • This expansion can be due oedema or infiltration of acute inflammatory cells (acute interstitial disease), or the accumulation of chronic inflammatory cells and fibrous tissue (chronic interstitial disease)
• Calyces, pelvis, ureter and bladder


  • Have same basic histologic structure
• Walls of ureter


  • Become gradually thicker with increased proximity to bladder
• Mucosa of these organs

  • Consist of transitional epithelium and a lamina propria of loose or dense connective tissue
• Surrounding the lamina propria


  • Is a dense, woven sheath of smooth muscle
• Facet cells


  Superficial cells of the transitional epithelium responsible for the osmotic barrier between urine and tissue fluids
• Muscular layers in the calyces, renal pelvis and ureters

  • Have a helical arrangement
• As the ureteral muscle cells reach the bladder


  1. They become longitudinal

  2. The intravesical part of the ureter is composed of longitudinal fibres which fan out distally to form the superficial trigone

  3. Whose muscles continue dorsally to the verumontanum in males and the external urethral meatus in females
• Muscle fibres of the bladder

  • Run in every direction until they reach the bladder neck, where 3 distinct layers can be identified:
  • Internal longitudinal layer - fibres form the true involuntary urethral sphincter
  • Middle layer - ends at bladder neck
  • Outer longitudinal layer - continues to end of prostate in males and external urethral meatus in females
• Ureters


  • Pass through the wall of the bladder obliquely, so that a valve is formed that prevents the backflow of urine to the kidneys
• Urethra


  A tube that carries the urine from bladder to exterior
• Male urethra


  • Prostatic part
  • Membranous part
  • Bulbous part
  • Pendulous part
• Female urethra


  • 4-5cm long tube
  • Lined with squamous stratified epithelium
  • Areas of pseudostratified columnar epithelium
  • Midpart is surrounded by an external striated voluntary sphincter
• Acute Nephritic Syndrome


  Glomerular syndrome dominated by the acute onset of usually grossly visible haematuria, proteinuria and hypertension.
• Nephrotic Syndrome


  Heavy proteinuria, hypoalbuminaemia, oedema, hyperlipidaemia, lipiduria
• Subtle or Mild Glomerular Abnormalities

  Asymptomatic haematuria/proteinuria, or a combination
• Acute Renal Failure


  dominated by oliguria or anuria

  can result from glomerular, interstitial or vascular injury or acute tubular necrosis
• Chronic Renal Failure


  Prolonged symptoms and signs of uraemia and is the end result of all chronic parenchymal diseases
• Renal Tubule Defects


  Dominated by polyuria

  Result of either diseases that directly affect tubule structure or defects in tubule function
• UTI


  Bacteriuria and Pyuria

  Infection may affect kidney or Bladder
• Renal Stones


  Cause renal colic, haematuria and recurrent stone formation
• Urinary Tract Obstruction and Renal Tumors

  Represent specific anatomic lesions with often varied clinical manifestations
• Cystic Diseases

  Heterogenous group comprising: hereditary, developmental but non-hereditary and acquired disorders. As a group they are important for several reasons:

  1. Reasonably common and often represent diagnostic problems for clinicians
  2. Some forms, like adult polycystic disease are major causes of chronic renal failure.
  3. Can occasionally be confused with malignant tumours.

   
• Urinary Tract Diseases

  • Chronic glomerulonephritis - most common causes of chronic renal failure
  • Glomeruli may be injured or caused by a disease.
  • Various types of glomerulonephritis are characterised by 1 of 4 basic tissue reactions.
  • Hyper cellularity
  • Cellular proliferation of mesangial or endothelial cells
  • Leukocytic (WBC's) infiltration
  • Basement membrane thickening
  • PAS stain.
  • Hyalinisation
  • Sclerosis
  • Accumulation of material that is homogenous and eosinophilic
• UTD Clinical Manifestations

  1. Acute nephritic syndrome
  2. Rapidly progressive glomerulonephritis
  3. Nephrotic syndrome
  4. Chronic renal failure
  5. Asymptomatic haematuria or proteinuria
• Tubules and Interstitiu

  Most forms of tubular injury involve the interstitium as well.

  2 major groups of processes:

  1. ischaemic or toxic tubular injury, leading to acute tubular necrosis and acute renal failure
  2. Inflammatory reactions of the tubules and interstitium, tubulointerstitial nephritis

   
• Acute Tubular Necrosis

  Characterised by destruction of tubular epithelial cells and decreased or loss of renal function

  Can be cause by:

  • Ischemia due to decreased or interrupted blood flow
  • Direct toxic injury to the tubule by drugs, radiocontrast dyes, myoglobin, haemoglobin and radiation
  • Acute tubulointerstitial nephritis caused by a hypersensitivity reaction to a drug
  • Disseminated intravascular coagulation
  • Urinary obstruction by tumours, BPH or blood clots

   
• Tubulointerstitial Nephritis

  Characterised by histologic and functional alterations that involve predominantly the tubules and interstitium.

  Can be acute or chronic

  • Acute has a rapid clinical onset and is characterised by interstitial oedema, leukocyte infiltration and focal tubular necrosis
  • Chronic is characterised by infiltration of mononuclear leukocytes, prominent interstitial fibrosis and widespread tubular atrophy

   
• Pyelonephritis

  Affects tubules, interstitium and renal pelvis and is one of the most common diseases of the kidney.

  Occurs in 2 forms:

  • Acute pyelonephritis - caused by bacterial infection and is renal lesion associated with urinary tract infection
  • Chronic pyelonephritis - more complex disorder, bacterial infection plays a role but other factors are involved.

  Ascending infection is the most common cause of pyelonephritis

   
• Blood Vessels

  Nearly all kidney diseases involve the renal blood vessels secondarily.

  Systemic vascular diseases, such as vasculitis, also affect renal vessels.

  Hypertension is linked to renal disease because kidney disease can be both the cause and consequence of inc. blood pressure.

  Recognition of urinary obstruction is important because obstruction increases susceptibility to infection and to stone formation and unrelieved obstruction almost always leads to permanent renal atrophy.

   
• Kidney Tumours

  Both benign and malignant

  Exception of oncocytoma, the benign tumours rarely cause clinical problems

  Malignant tumours on the other hand, are of great importance clinically

  By far the most common of these malignant tumours is the:

  • Renal cell carcinoma, followed by
  • Wilms tumour, found in children

   
• Benign

  Renal Papillary Adenoma:

  • Small, discrete adenomas arising from the renal tubular epithelium are found commonly (7-22%) at autopsy
  • Most frequently papillary.

  Renal Fibroma:

  • Usually found at autopsy, small foci of grey-white firm tissue, usually less than 1cm in size.
  • Located within the pyramids of the kidneys.

  Angiomyolipoma:

  • Consists of vessels, smooth muscle and fat.
  • Present in 25-50% of patients with tubular sclerosis

  Oncocytoma:

  • An epithelial tumour composed of large, eosinophilic cells with a small round nuclei.
  • Arise from intercalated cells.
• Malignant

  Renal cell carcinoma:

  Arise from tubular epithelium and are therefore renal adenocarcinomas.

  Represents about 1-3% of all visceral cancers and amount for 85% of renal cancers in adults.

  Occurs most often in older individuals, usually in the sixth-seventh decades of life, showing a male preponderance in the ratio of 2-3:1

  Most renal cancers are sporadic, but unusual forms of autosomal-dominant familial cancers occur.

   

  4 types of renal cell carcinomas:

  1. Clear cell carcinoma
  2. Papillary carcinoma
  3. Chromophobe renal carcinoma
  4. Collecting duct carcinoma
• Clear Cell

  Most common

  Accounts for 70-80% of RCCs

  On histologic examination, the tumour are made up of cells with clear or granular cytoplasm.

  Non-papillary